It is often helpful in the glass industry, as well as other transparent medium industries, to detect the presence and surface location of conductive coatings that are applied to the surface of the non-conductive medium. Some of these coatings are classified as low emissivity (low E) coatings. These coatings are typically not visible and therefore difficult to detect without electronic assistance.
The Klopfenstein U.S. Pat. No. 5,132,631 (which was assigned to the same assignee as the present invention), can be used for identifying the presence of the coating on the medium. It has been found, however, that in situations where two mediums are separated by a gap (for example, a dual pane window assembly), the Klopfenstein '631 device must be calibrated for a pre-determined range within a narrow range of gap thicknesses for a given thickness of the mediums. One limitation of Klopfenstein '631 device is that the calibrated ranges for glass and gap thickness are quite narrow and do not aptly cover the variations that are experienced in the glass industry. This is of concern since the flat glass industry generally utilizes glass from about 2.2 mm up to about 10 mm. For example, flat glass used in residential applications is typically in the 2.2 mm to 4 mm range, while flat glass used in commercial applications is typically in the 5 mm to 10 mm range. In addition, in all of these applications, there is also a large variation in the gaps that are placed between the two substrates. Typical gaps in the flat glass market ranges from ¼″ to ⅞″.
Another limitation of the Klopfenstein '631 device is that it is difficult to achieve the desired accuracy of measurements when glass thickness and gap separating the two mediums vary from application to application. That is, different combinations of glass and gap thicknesses cause the resulting Klopfenstein-measured values to overlap from coated to uncoated test samples, causing the Klopfenstein '631 device to yield incorrect results. This is illustrated in FIG. 1 which contains a chart showing a variety of capacitance measurements with a variety of glass and gap thickness combinations.
FIG. 1 clearly shows the number of applications that overlap causing incorrect test results to occur when using the Klopfenstein '631 device. That is, the Klopfenstein '631 device is unable to differentiate the correct results across a variance in glass or gap thickness. For example, if the Klopfenstein '631 device is calibrated to measure 3/32″ glass, but the user is testing ¼″ glass, the measured capacitance values from varying glass and gap thicknesses overlap, causing incorrect test results from the calibrated invention.
FIG. 1 also shows that two pieces of 3/32″ glass with a low E coating resting on surface 3 of the 4 possible surfaces (where two pieces of glass are separated by an gap of ½″) (see arrow of left side of chart), will result in a capacitance value of 750. In the case where a Klopfenstein '631 device that is calibrated to measure 3/32″ glass, such device would correctly indicate the coating is on the FAR surface.
However, in another example, a single piece of ¼″ glass will result in a capacitance value of 725 (bottom arrow on right), while two pieces of ¼″ CLEAR glass separated by ½″ will result in a capacitance value of 775 (top arrow on right). This then indicates that the single piece of ¼″ glass has a capacitance below the 3/32″ double pane example, while the ¼″ double pane clear combination has a capacitance above the 3/32″ double pane example.
These examples illustrate that different thicknesses of glass, as well as different numbers of glass panes, both coated and uncoated can all result in similar capacitance values that cannot be sufficiently differentiated by the Klopfenstein '631 device. Thus, for both of the ¼″ combinations of glass, the Klopfenstein '631 device would incorrectly identify these glass combinations as also have a coating on the FAR surface.
Consequently, the Klopfenstein '631 device is not capable of differentiating the correct low E surface location across a mix of glass and gap thicknesses.
It is to be noted that the glass combinations chosen for the example above are extremely common in the flat glass industry. It is also to be noted that these examples would apply to additional sensing techniques beyond capacitive plates, such as inductive sensors.
Therefore, there is a continuing need for an improved, reliable and efficient method and device to detect the presence, location and type of coating applied to various media.